The invention set forth in this specification primarily relates to small portable transmitters which are primarily intended to be used to broadcast a signal in response to what is referred to herein as "external actuation."
This term "external actuation" is employed in this specification to designate any of a large number of different items such as movement of a transmitter, movement of an object adjacent to a transmitter, undue heat, or vibration. It is frequently desirable to utilize portable transmitters which are sensitive to one or more such external actuations in the sense that they will broadcast a signal in response to such external actuation in various alarm type applications. Thus, for example, portable transmitters which are responsive to such actuations can be mounted on or adjacent to doors, windows, floor mats, or the like in order to detect intrusions such as normally accompany a burglary. These portable transmitters may also, however, be utilized to detect a fire or some other physical condition and to broadcast a signal indicating the presence of a fire or such other condition.
Portable transmitters for these applications preferably are comparatively small units of a self-contained character. When portable transmitters as indicated are relatively small in dimension and carry a small battery as a power supply they may be easily used in a number of different ways. It is presently considered most preferable to utilize these units by adhering them through the use of tape or other related mounting means in various operative locations. The portable transmitters of the present invention are to be utilized in this manner. They preferably are constructed as small packages having flat mounting surfaces which can be easily transported and installed.
It is commonly considered that comparatively small portable transmitters are inherently somewhat limited in their performance characteristics because of their size. One factor which is related to this involves the efficiency of an antenna incorporated within a portable transmitter as indicated. It is normally desired that any antenna used have an effective radiant pattern and that such an antenna be capable of broadcasting an RF signal over as large an area as reasonably possible per unit of power consumed. This problem of providing suitable antennas for use in small portable transmitters is further complicated because of the need to utilize simple metal coil or loop antennas in these units because of economic as well as constructional considerations.